Electrical current can be measured by connecting a current meter in series with the wire. In many cases, however, disconnecting the wire to connect the current meter can be inconvenient. For example, the wire can be tightly grouped in a bundle with several other wires making it difficult to individually disconnect the wire of interest. Another example of the inconvenience is where a terminal to which the wire is connected is not conveniently located or is inaccessible, requiring the wire to be cut for the current meter to be connected in series. It is time consuming to reconnect the two ends of the cut wire after a measurement is taken, and can be dangerous in situations where relatively high current is carried by the wire. Additionally, the integrity of the wire is compromised by cutting and reconnecting, thus, potentially raising reliability problems.
A clamp probe connected to a conventional multimeter can be used to measure electrical current without the need for disconnecting a wire. The clamp probe is opened, the wire is inserted into the clamp, and the clamp is closed to take a current measurement. The closed clamp includes a core of ferromagnetic material, which when closed, represents the core of a transformer. The wire passing through the clamp represents the primary winding. As known, a current flowing in the wire induces a magnetic flux in the core of the transformer, which in turn, induces a current in a secondary winding of the transformer. Using this physical phenomena, the magnitude and polarity of the current in the clamped wire can be determined based on the current induced in the secondary winding and the characteristics of the transformer formed by the clamped wire.
As previously discussed, a clamp probe can be connected to a multimeter having current measuring capabilities for taking current measurements. The clamp probe is typically connected to the multimeter through wires that connect to plug-in terminals. A benefit to this arrangement is that the clamp probe can be clamped to the wire and the meter positioned so that a technician can conveniently view the measured value, which is especially useful when the wire is located in a difficult to reach location. However, two hands are typically necessary to take a measurement: one to put the clamp in place and another to hold the meter while taking a measurement. Additionally, since the clamp probe is an attachment to the multimeter, it is typically stored separately from the meter, which can be inconvenient when carrying the equipment around and can also be easily misplaced when not used.
As an alternative to a separate probe and meter arrangement, clamp meters are designed with the clamp integrated into the body of the meter, which can provide the convenience of taking a measurement using one hand. That is, only one hand is used to open and close the clamp for clamping a wire and to take a current reading. Additionally, with the clamp integrated into the body of the meter, there is no possibility of misplacing the clamp or having any difficulties transporting the equipment.
“One-handed” clamp meters are generally acceptable for applications where the display can be easily viewed by the technician with the meter clamped to the wire for measurement. However, problems with reading the measurement can arise where the wire is difficult to reach or is positioned such that the display of the meter is obscured when the meter is in position for measurement. In order to take a measurement in these situations, a technician can quickly check the display by forcing himself into an awkward position just long enough to view the display, or where the meter has a feature which captures a measured value on a display, the technician can remove the meter from the awkward or obscured position after the measurement is taken and view the captured measured value. These solutions have obvious disadvantages. In one case, the technician must put himself in a physically uncomfortable and potentially dangerous position when attempting to view the measured value on the display of an awkwardly positioned meter. In the other case, removing the meter from a wire that was difficult to clamp in the first place is inconvenient and can be time consuming if the clamp meter must be re-clamped to take additional measurements from the same wire. Additionally, where real time measurements are desired, such as measuring start-up currents or detecting intermittent current loading, the meter must be kept in place during continuous measurement.
A meter having a remote clamp probe, such as using a clamp probe coupled to a multimeter as previously described, can be used to address the problems with awkward to reach or difficult positioned wires by clamping the wire with the remote clamp, and having the meter positioned in a convenient location for reading the measured values. However, in addition to the disadvantages previously discussed, these meters also lack the convenience of one-handed measurements for applications where it is possible to do so. A solution to the problem is for a technician to have both types of meters in order to have the benefits of each design. This is a costly solution since two different meters need to be purchased, although only one meter is typically used at a time for taking a measurement.